Turbochargers are well known devices for supplying air to the intake of an internal combustion engine at pressures above atmospheric, commonly called “boost pressures” and are widely used in all forms of vehicles.
A conventional turbocharger includes a turbine rotor or wheel with a plurality of fins inside a volute turbine housing. The turbine rotor is rotated by exhaust gases from the engine which impinge upon the turbine fins. The rotor, via a connecting shaft, provides the driving torque to a compressor. Ambient air fed to the compressor creates a boost pressure that is fed to the intake manifold of the engine. The flow capacity of the exhaust turbine is a function of the casing volute areas, and the passage of the exhaust gases as it strikes the turbine fins. The flow of exhaust gas has to be regulated to control the compressor speed to create the desired boost in manifold pressure.
A typical centrifugal compressor includes an impeller driven at high speed by the turbine rotor. A diffuser surrounding the impeller causes the ambient air to increase in pressure which is directed to the intake manifold.
One particular goal with any turbocharger is the need for a quick response, i.e., prevent time lag or a delay between the time when high power output is first demanded of the engine by setting the throttle to a wide open position and the time when a boost in the inlet manifold air pressure is delivered by the compressor. In some instances a time lag could result in a dangerous driving situation when substantially instantaneous response is desired.
Others have proposed variable geometry turbines and moveable vanes for guiding, dividing, or changing the direction the exhaust gases relative to the to the turbine rotor and thereby control its rotational speed.
U.S. Pat. No. 4,893,474 describes a pivoting valve member that is actuated by a spring loaded bell-crank lever to control a wastegate valve to vent the exhaust passages. Wastegates are often used in turbochargers to open at high speed to bypass a portion of the exhaust gas flow in the turbine to keep the speed of the turbocharger low and thereby maintain the intake manifold pressure below a given critical value.
U.S. Pat. Nos. 4,510,754 and 6,073,447 teach the use of separate first and second passages, of differing cross-sections, for the passage of exhaust gases into the volute. The passages being selectively opened and closed by a flapper valve and associated control system.
U.S. Pat. Nos. 4,565,068 and 4,927,325 describe an inlet opening to the volute with a concentric divided partition and a plurality of concentric fixed individual wall segments arranged in the direction of flow. The space between the wall segments create orifices to contribute uniform impingement on the turbine rotor.
U.S. Pat. No. 4,729,715 provides at least one or a plurality of moveable wall members to vary the passage area, yet allowing the whole flow of exhaust gas through the volute. The wall member is a vane that includes a passage between the front and rear of the vane that becomes a nozzle to aid in distributing the passage of gas in the volute.
Others such as U.S. Pat. No. 4,179,247 have proposed variable area turbines (VAT) or U.S. Pat. No. 6,272,859 a variable geometry turbine (VGT) with variable nozzle vanes or with turbine vanes individually pivotal.
Such devices usually require complex turbine volute housings and control means.